1. Field of the Invention
This invention relates to a method and apparatus for linearly scanning an energy source over an array of optical fibers. More particularly, the present invention allows a series of energy pulses to be directed into different predetermined linearly-arranged segments of the optical fiber array.
2. Description of the Prior Art
The use of radiant energy sources, such as lasers, in medical procedures is presently attracting great attention. For several decades, scientists have described the use of lasers to ablate tissue. Suggested applications have included removing hair, corneal surgery, removing port wine stain and removing plaque from blood vessels. For example, percutaneous transluminal laser angioplasty involves the introduction of a catheter containing a bundle of optical fibers, into a blood vessel. The distal end of the catheter is positioned next to an obstruction in the blood vessel. Laser energy is applied to the optical fibers to ablate the obstruction. To be effective, each fiber in the bundle must carry laser energy having sufficient fluence (energy per unit area) to ablate tissue. Furthermore, laser surgeons have recognized the desirability of removing as large an area of the obstruction as possible without excessive manipulation of the catheter. This calls for a large number of optical fibers within the catheter. When laser radiation with a sufficiently high fluence is applied to a number of fibers simultaneously, a large amount of laser energy is introduced into the body. The body is traumatized by such energy. In fact healthy tissue can easily be damaged. At the same time, a large and costly laser is required to produce the large amount of energy.
Prior to this invention the seemingly contradictory goals of applying laser radiation of sufficient fluence over a relatively large area, while at the same time reducing the peak total energy applied to the body had not been realized.
Kittrell et al. U.S. Pat. No. 4,913,142 teaches a laser angioplasty system including a catheter housing a bundle of optical fibers. The multiple fibers allow the selection of tissue to be removed. Selectivity is achieved by monitoring spectroscopic characteristics. Each fiber of the bundle may be arranged in a linear array. Either the array or the laser energy is movable to allow each individual fiber to be selectively irradiated. First, low level energy is applied to each individual fiber in sequence and reflections from tissue proximate the distal end of the fiber are monitored to distinguish healthy tissue from tissue to be ablated. Then, high fluence laser energy is sequentially applied to one fiber at a time and only to those fibers illuminating tissue to be ablated. Nowhere in this patent is there any suggestion of the desirability or even the possibility of grouping more than one of the optical fibers making up the array for simultaneous irradiation. In fact, such an arrangement would destroy the fundamental function and purpose of the system described in the patent.
Alster U.S. Pat. No. 4,614,868 teaches an imaging system in which a laser beam can be scanned over a fiber optic bundle by irradiating fibers singly or in groups of fibers, the groups being as large as the spot size of the laser beam. However, this patent fails to suggest that scanning a laser beam, having sufficient fluence to ablate tissue, over a linear array of optical fibers is advantageous in reducing the total energy delivered or in reducing the size of the laser required.
Simon et al. U.S. Pat. No. 4,007,377 discloses an optical scanning system for use with universal product codes. A series of optical components, including a galvanometer, is used to expand the laser beam to illuminate an entire bar code. There is no suggestion of how a scanning system may be employed to maintain a sufficiently high fluence yet reduce energy in an ablation system.
Hotchkiss discloses, in U.S. Pat. No. 3,984,171, a linear scan system that provides a vertically and horizontally defined continuous linear scan of predetermined length. Even though Hotchkiss discloses a device that appears to be able to scan in a linear manner, there is certainly no suggestion to irradiate selected groups of optical fibers sequentially.
Chande U.S. Pat. No. 4,838,631 teaches a laser beam directing system for directing successive beam pulses of a pulsed laser into different optical fibers. This invention is especially useful with laser systems used in manufacturing and especially for use where a single laser is shared between several manufacturing workstations. There is no teaching that the device has any use in the medical field. This patent fails to suggest that scanning a laser beam, having a sufficient fluence to ablate tissue, over a linear array of optical fibers is advantageous in reducing the total energy delivered or in reducing the size of the laser required.